Formatter: Better support for explicit line breaks

[sporto]

When writing html, it is common to have line breaks for block elements. This makes the code easier to scan.

e.g.

<div>
  <div>A</div>
  <div>Something longer</div>
</div>

However when converted to Gleam, something like this ends up being

html.div(
  [],
  [html.div([], [text("A")]), html.div([], [text("Something longer")])],
)

The shape of the code seldom matches the shape you would have on manual written html.

e.g. people don't write this:

<div>
  <div>A</div><div>Something longer</div>
</div>

I really like using functions for html, but the formatting makes the html difficult to understand. I think that if the formatter would respect my line breaks, it would contribute to remove strangest budget.

Related issue #1117